The present invention is in the field of non-invasive measurements of physiological parameters of patients, and relates to a device for the enhancement and quality improvement of blood-related signals.
Non-invasive methods for measuring various blood-related parameters have become very popular due to the fact that these measurements, in distinction to invasive ones, do not involve the physical withdrawal of a blood sample from the patient""s body. Non-invasive measurements are based on the pulsatile nature of arterial blood, and utilize optical monitoring techniques capable of detecting such pulsatile blood behavior. Results obtained from pulse measurements can be used for determining various physiological parameters such as blood oxygen saturation, hematocrit, the concentration of hemoglobin, glucose, carbon dioxide, arterial blood pressure, etc.
The optical monitoring techniques of the kind specified typically utilize the detection of light transmitted or reflected from different locations on a patient""s body. According to some of these techniques, disclosed for example in U.S. Pat. No. 5,101,825 changes in the blood parameters at a specific location are measured as a function of changes in the blood volume at this location. Other techniques, disclosed for example in U.S. Pat. No. 5,499,627, utilize impedance measurements.
Various methods aimed at increasing the natural pulsatile signal of a patient for effecting non-invasive optical measurements have been developed. These methods are disclosed for example in the following patent documents: DE 19629342, U.S. Pat. No. 5,638,816. WO 9843096 and in U.S. patent application Ser. No. 09/468,178, which is a co-pending application assigned to the assignee of the present application.
According to the above methods, the natural pulse signals are either detected and used for measurements, or created by performing various suitable procedures which are typically based on the use of a probe applied to the patient""s finger (pulse oximetry) or other extremities. These methods typically require well-established, stable and reproducible capillary, venous and arterial blood presence at the location under measurement. As known, to meet such a requirement, a slight pressure may be applied to the soft tissue in the vicinity of the measurement location. A pressure-inducing holder used in such a measurement probe is usually a part of the probe itself, i.e., is associated with a specific sensor used in a specific measurement device.
Some of the conventional measuring devices utilize folded adhesive sensors, namely disposable adhesive sensors with optics embedded therein. For example, U.S. Pat. No. 5,170,786 discloses a reusable probe system aimed at enabling to reuse the sensor element, which are the most expensive part of a probe system, and dispose a positioning substrate. In this probe system, the sensor elements are thus made separable from the flexible substrate, which is to be brought into contact with the patient""s skin, and is formed with apertures to fasten a light source and light sensor in stable disposition on the skin. EP 0313238 discloses a pulse oximeter sensor constructed so as to reduce signal loss due to thermal vasoconstriction and ambient light interference. The sensor utilizes a wrap of a disposable elongated configuration and includes a sheet of metalized material. A light source and a detector are aligned with the wrap.
U.S. Pat. No. 5,452,717 discloses a sensor probe, in which a source of electromagnetic radiation and a detector are supported on a carrier having a flexible body to at least partially surround a portion of the tissue under measurements All elastic sheath is coupled to the carrier by its one end, and has the other end of a tubular shape rollable upon itself to surround at least a portion of the carrier, with the carrier positioned over the portion of tissue.???
Other devices utilize non-disposable sensors in the form of a clip to be placed on the patient""s finger and fixed by a spring. Elastic cushions support the optical elements and prevent slipping of the sensors off the finger.
The inventors have found that the application of homogeneous, even pressure to a body part to which measurements are to be applied results in the enhancement and quality improvement of blood-related signals from the body part. However, the existing disposable devices fail to provide homogeneous pressure applied to the patient""s finger. As a result, even pressurization of the finger tissue cannot be achieved. Furthermore, none of the existing devices can be used solely for the enhancement and quality improvement of blood-related signals, regardless of the measurement technique being used. For example, adhesive sensors are applicable to the pulse-oximetry technique based on the detection of optical signals, while being unsuitable for the impedance-based or a similar technique.
A pressure-inducing element can be applied to the patient""s finger prior to the measurement itself, so as to create the required preconditions for starting blood-related measurements. To this end, it is desirable to have a pressure-inducing holder that would be applicable for a patient""s finger, irrespective of a patient""s individual peculiarities, and that would be useful with a non-invasive measurement device of any kind.
There is accordingly a need in the art to improve conventional techniques for measuring blood-related signals by providing a novel disposable and quickly mountable/removable device for applying to the patient""s finger or toe so as to enhance blood-related signal and improve the quality of the signal.
The main idea of the present invention consists of providing such a disposable device, which, when being applied to the patient""s finger or toe (i.e., being wrapped around the finger/toe portion), is capable of providing even pressurization of the wrapped portion including the finger/toe tip, and can be used with a sensor of any suitable known kind capable of detecting the blood-related signal to measure any suitable parameter that can be derived therefrom.
There is thus provided according to the invention, a disposable, removable device for applying to a patient""s finger or toe for non-invasive measurements of blood-related parameters derived from a response of a measurement location in the finger or toe to a predetermined external field, wherein:
the device comprises a cover for wrapping at least a portion of the finger or toe including a tip portion thereof in a manner to provide even pressurization of the entire wrapped portion with a pressure less than systolic pressure, thereby providing enhancement and quality improvement of measured signals;
said cover is elastic, has a substantially circular cross-section, and is shiftable along a longitudinal axis of the finger or toe between an inoperative folded position of the cover and an operative extracted position of the cover, in which it wraps the finger or toe portion including the tip portion, and provides said even pressurization of the entire wrapped tissue with the pressure being less than systolic pressure;
at least a portion of the cover is made of a material enabling said non-invasive measurements of the blood-related signal therethrough.
The elasticity of the cover may be such that the cover itself desirably presses the finger/toe tissue whilst wrapping the finger/toe portion. Alternatively, or additionally the device may comprise a pneumatic device or a mechanical device, e.g., a pressing ring to be placed on tee finger/toe above the cover. By operating such a device, e.g., by twisting the ring, the desired pressure can be established.
The elasticity of the cover and its small thickness provides slight and even pressurization (which is less than systolic blood pressure) on the tissue within the covered finger portion including the fingertip. This results in the enhancement of the pulsatile and non-pulsatile blood-related signals, prevents blood flow disturbance during measurement, and stabilizes the finger tissue during measurements, thereby improving the quality of the measured signals.
Preferably, the device also provides a heating effect to heat the wrapped finger/toe portion up to a desired temperature (about 38xc2x0 C.), thereby enhancing the blood-related signal even more The heating ability of the device increases the accuracy of the non-invasively derived blood-related parameters such as blood oxygen saturation, blood pressure, hemoglobin, glucose, cholesterol and other analyte concentrations. The shrinkage effect by heating the cover affects tissue pressurization.
According to another aspect of the present invention, there is provided a method for obtaining enhanced and quality improved blood-related signals from a portion on a patient""s body, the method comprising the steps of:
(i) applying a pressure, substantially less than a systolic pressure, to said portion in a manner to provide even pressurization thereof;
(ii) applying sensor means to a measurement location within the pressed portion, the sensor means being capable of applying an external field to said measurement location, detecting a response of the measurement location to said external field indicative of blood-related signals, and generating data representative thereof.
The external field to be applied to the measurement location may be electromagnetic radiation. In his case, the sensor means may utilize an illumination assembly for illuminating the measurement location with incident radiation, e.g., near infra-red (IR) radiation of having a wavelength of 600-2000 mm, and a detection assembly for detecting a light response from the illuminated location. The location of the detection assembly depends on the kind of response that is to be detected, i.e. reflected or transmitted signals.
It should be understood that in order to enable the application of such a radiation-based sensor means, the cover should be formed with means enabling light propagation therethrough. To this end, the entire cover may be transparent with respect to the incident radiation (e.g., near IR radiation). In this case, the cover should be of a sufficient thickness (i.e., practically about 0.1-0.2 mm and preferably not exceeding 50 xcexcm) so as to prevent collection by the detection assembly of incident radiation rounding the wrapped portion, while allowing the detection of the signal response.
Alternatively when a thicker cover is used (e.g., of 0.5 mm in thickness), the cover may be formed with at least one optical window transparent for near IR radiation, thereby enabling the application of the sensor means to a location within the wrapped portion below the window. If the transmitted signal is to be detected, two optical windows should be provided made at opposite sides of the cover. Should the reflected signal be detected by the sensor means, the provision of only one optical window is sufficient for measurements, but two spaced-apart optical windows located at the same side of the cover can be used. The non-transparent regions of the cover absorb light waves going around the cover"" material thickness and through the skin of the wrapped portion, and prevent these waves from being collected by the detection assembly. This increases the signal-to-noise ratio of the detected signal.
The non-transparent regions can be manufactured from the same material as that of the transparent regions, but with additional pigments such as carbon, titanium oxide, BaS, BaSO4, etc. that make these regions non-transparent for near IR radiation. Materials suitable for the manufacture of the cover are silicon, latex and other flexible, elastic and transparent for near IR radiation materials.
More specifically, the present invention is useful with non-invasive measurements on a patient""s finger, and is therefore described below with respect to this application